It has become common to treat a variety of medical conditions by introducing an implantable medical device partly or completely into the human body. For example, orthopedic devices are commonly inserted into joints such as the knee, spine, shoulder and the like. Additional orthopedic devices are often implanted adjacent bone such as metal plates during fracture repair and spinal rods for the re-alignment of the spine. Many other implants are used for implantation into the esophagus, trachea, colon, biliary tract, urinary tract, vascular system or other locations within a human or even a veterinarian patient.
One disadvantage associated with implantable medical devices, especially titanium and titanium alloy devices, is microbial adhesion to titanium surfaces. Microbial adhesion occurs when unwanted microorganisms adhere to the orthopedic implant either during implantation or afterwards. Microbial adhesion to the surface of an implant device that eventually lead to biomaterials-related infections is a well-recognized complication of implant materials and devices. Once adhesion has occurred, proliferation of the microbial agents leads to the development of a biofilm, which is unsusceptible to most therapeutic agents at achievable concentrations. Thus, the course of microbial infection involves three major steps: microbial adhesion; microbial proliferation; and formation of a bacterial bio-film.
Typically metal implants are passivated by a known process. First, the metals to be passivated are washed using a detergent for 40 minutes in an ultrasonic bath at 65 degrees C., followed by de-ionized water rinsing in an ultrasonic bath at 65 degrees C. The metals are then passivated by immersing them in 30% Nitric acid solution at room temperature or a temperature below 100° for 30 minutes. After the passivation, the parts are rinsed with de-ionized water in an ultrasonic bath for 15 minutes at Room temperature; followed by neutralization by immersing the parts in sodium bicarbonate solution at room temperature for 13 minutes. After the neutralization process, the parts are then rinsed in de-ionized water in an ultrasonic bath at room temperature for 15 minutes. The parts are then rinsed with isopropyl alcohol and finally dried in air at room temperature for few hours. Passivation treatments provide a controlled and uniformly oxidized surface state. The passivation leads to a dense and stable oxide film and improves corrosion resistance (decreases ion release). It has however practically no influence on the overall surface topography of titanium surface. The resulting layer of this chemical treatment is a TiO2 film in a thickness of two to six nanometers.
The main difference between the “nano-modification process” of the present invention and the current passivation processes is the heating process involved in the nano-modification process after the acidic treatment. In the typical passivation process the nitric acid treatment changes the oxygen content of the surface, but returns to normal after drying. In the process of the present invention the acid treatment is followed by a heat treatment at an elevated temperature (greater than 100° C.) which creates the desirable nanofeatures on the implant surface that decrease bacterial response.
Therefore, these implants contain antimicrobial properties which reduce microbial-related infections.